Christopher O'Dell over at grognadling is doing a great series, reading through the (re-printed) AD&D Dungeon Masters Guide for the first time and posting his thoughts.
The DMG has a much-deserved reputation for being a book you can read again and again, always getting something new out of it. That's really for two reasons, in my opinion:
1) it's chock full of really good stuff.
2) it's opaque and poorly organized.
So you can read it again and again and get new stuff out of it, but that's because you really have to read it again and again to find all the stuff in it. Or perhaps just take notes as you go like Grognardling. That's the cool thing about his series, really - for me it's to imagine what it was like to read that book with completely fresh eyes, but adult ones.
The 1st edition DMG was the first AD&D book I owned, purchased from Jamesway for $12 when I was like 9 or 10. So it has a special place in my heart even as I sometimes rail against it. It was hugely influential on my own play and how my friends played. And yes, we'd take it out and point out passages to each other while arguing over how the game was supposed to be played - because if Gary Gygax made one thing clear, there was a right way to play AD&D. 4th graders aren't exactly going to take this to mean "the rules are guidelines." The somewhat random organization of the book and the authorial tone influenced my own writing a lot. At first I copied the style, until it was beaten out of me in college. To some extent, anyway. And when I write for game books, I'm careful to avoid that high-handed "right way" approach and prize clarity and organization over stern warnings about players not reading the books. I don't hate the book - I still take it down and use stuff for it for my non-AD&D games - but I try to remember its lessons both good and bad.